1. Field of the Invention:
The present invention relates to a fluid-sealed mounting having therein a chamber in which a fluid is sealed, and more particularly to the structure of a fluid-sealed mounting for connecting an engine or a torque rod or radius rod in a wheel suspension to a vehicle body frame.
2. Description of the Prior Art:
One known type of fluid-sealed mounting such as an engine mounting comprises a base adapted to be connected to a vehicle body frame, an attachment adapted to be connected to a source of vibrations such as an an engine, a shearing elastic member of rubber joined between the base and the attachment, and a diaphragm attached to the base. The base, the attachment, the elastic member, and the diaphragm jointly define a fluid chamber in which there is transversely disposed a partition having an orifice and mounted on the base. A fluid is sealed in chambers divided by the partition. Such a mounting is disclosed in Japanese Laid-Open Patent Publication No. 56-153133.
Generally, it is known that a fluid-sealed mounting used as an engine mounting can produce an ideal damping force when an energy loss coefficient (tan .sym.) is about 0.3 at a vibration frequency in the range of from 10 to 15 Hz. If the energy loss coefficient tan were smaller than 0.3, the mounting would have a small vibroisolating effect on vehicle vibrations. If the energy loss efficiency is greater than 0.3, a dynamic spring constant would become higher, and the vibroisolating capability for isolating secondary vibrations and the like would be reduced.
With the above known fluid-sealed mounting, the rate of flow of the fluid passing through the orifice in the partition between the two chambers is large, resulting in an energy loss coefficient tan .delta. ranging from 0.4 to 0.6. The value of tan .delta. at the vibration frequency of 15 Hz is 0.52 rather than the desired value of 0.3. The conventional fluid-sealed mounting is also disadvantageous in that when the attachement is subjected to an abrupt tensile load, the fluid pressure in the fluid chamber composed of the two chambers connected through the orifice is lowered since the rate of the fluid flowing through the orifice is high, and hence cavitation is generated in the orifice, thus failing to produce sufficient damping forces. As a consequence, the prior fluid-sealed mounting is not suitable for use as a mounting for a torque rod or a radius rod used in wheel suspensions.